2-stage fluidized bed type fine iron ore reducing apparatus, and reducing method using the apparatus

ABSTRACT

A two-stage fluidized bed reducing apparatus and a reducing method for fine iron ore of a wide particle size distribution with an increased degree of utilization of the reducing gas. Fine iron particles dropping through the holes of a gas distributor can be recycled into the fluidized bed furnace, thereby preventing an impediment of the reducing gas flow due to abnormal defluidizing or channeling. A first fluidized bed furnace dries, pre-heats and pre-reduces the fine iron ore, and a second fluidized bed furnace finally reduces the pre-reduced iron ore. Downstream of the respective fluidized beds are installed intermediate hoppers and gas/solid sealing valves. Thus, the fine iron ore particles which drop through the holes of gas distributors during the abnormal operation are recycled to the furnaces. Accordingly, the gas flow is not impeded.

FIELD OF THE INVENTION

The present invention relates to a 2-stage fluidized bed fine iron orereducing apparatus and a reducing method using the apparatus, forreducing a fine iron ore of a wide particle size distribution. Morespecifically, the present invention relates to a 2-stage fluidized bedfine iron ore reducing apparatus and a reducing method using theapparatus, in which a fine iron ore of a wide particle size distributioncan be reduced in an economical and efficient manner, and impediment ofthe reducing gas flow due to the abnormal phenomena such as defluidizingand channeling can be effectively avoided during the operation.

BACKGROUND OF THE INVENTION

In the conventional blast furnace method, the size of solid particlesare very large, and therefore, the iron ore can be reduced within afixed bed type furnace. However, in the case of a fine particle ironore, if the gas velocity is low as in the fixed bed type furnace, lowgas permeability and the sticking phenomenon occur, with the result thatthe operation may be halted. Therefore, a fluidized bed type method hasto be necessarily adopted, so that the movements of solid particles canbe made brisk with excellent gas permeability.

An example of the fluidized bed type furnace is disclosed in JapaneseUtility Model Publication No. Sho-58-217615. This is illustrated in FIG.1. As shown in FIG. 1, this furnace includes a cylindrical reducingfurnace 91 and a cyclone 95. The reducing furnace 91 is provided with araw iron ore feeding hole 92, a high temperature reducing gas injectinghole 93, and a reduced iron discharge hole 94. Further, in the lowerportion of the reducing furnace, there is disposed a gas distributor 96.A reducing gas is supplied through the gas distributor 96, and a fineiron ore is supplied through the feeding hole 92. Then the reducingfurnace is agitated, so that the fine iron ore and the reducing gas canbe mixed so as for the iron ore to be reduced in a fluidized state.After the elapsing of a time period, if the fluidized bed rises up tothe height of the discharge hole 94, then the reduced iron is dischargedthrough the discharge hole 94. Here, the fluidized bed takes the form ofa bubbling fluidized bed in which the reducing gas forms bubblings, andthe bubblings grow while passing through the particle layer.

In the above described reducing furnace, however, in view of theproductivity and economy, if the elutriation loss of the fine iron oreparticles is to be diminished, if the gas consumption rate is to beminimized, and if the gas utilization degree is to be maximized, thenthe particle sizes of the raw iron ore particles have to be strictlylimited. Accordingly, a fine iron ore having a wide particle sizedistribution cannot be handled. That is, the above described fluidizedbed type furnace cannot treat an iron ore of a wide particle sizedistribution, but can use only 0-0.5 mm, 0.5-1 mm, 1-2 mm and the like.However, the actually available fine iron ore particles have a size of 8mm or less. Therefore, if the naturally available fine iron ore is to beused, the fine iron ore has to be sorted by sieving, or it has to becrushed into the rated sizes. The result is that the productivity islowered, and the production cost is increased, because it requiresadditional process steps and additional facilities.

In an effort to solve this problem, Korean Patent No. 117065 (1997)proposes a 3-stage fluidized bed type reducing apparatus having taperedfurnaces as shown in FIG. 2. In this apparatus, a stable fluidizing ofan iron ore of a wide particle size distribution is aimed at, and forthis purpose, tapered furnaces are employed. Further, in order toimprove the reduction rate and the gas utilization rate, first the ironore is pre-heated, second pre-reduced and then finally reduced, therebyforming a 3-stage reducing process. That is, as shown in FIG. 2, anupper reaction vessel 10 pre-heats the iron ore in a bubbling fluidizingstate. A middle reaction vessel 20 pre-reduces the iron ore in abubbling fluidizing state. A lower reaction vessel 30 finally reducesthe pre-reduced iron ore in a bubbling fluidizing state, therebycompleting a continuous 3-stage fluidized bed type process.

In FIG. 2, reference codes 40, 50 and 60 indicate cyclones, referencecode 70 indicates a hopper, and 80 indicates a melter-gasifier.

In this 3-stage tapered fluidized bed type reducing furnace, an iron oreof a wide particle size distribution can be stably fluidized, and thereduction degree and the gas utilization degree can be considerablyimproved, compared with the conventional single type cylindricalfluidized bed type furnace. However, this furnace employs 3 stages, andtherefore, the facility cost is very high. Further, if a problem occursin any one of the plurality of the reaction vessels, then other reactionvessels are affected, with the result that the total process isadversely affected. Thus if an abnormal phenomenon such as defluidizingor channelling occurs which is actually very frequent, then the fineiron ore particles drop through the holes of the gas distributor to beagglomerated at the bottom of the reaction chamber. Therefore, the gasflow is impeded, and this cannot be prevented.

SUMMARY OF THE INVENTION

The present invention is intended to overcome the above describeddisadvantages of the conventional techniques.

Therefore, it is an object of the present invention to provide a 2-stagefluidized bed fine iron ore reducing apparatus, and a reducing methodusing the apparatus, in which the degree of utilization of the reducinggas is increased, an iron ore of a wide particle size distribution canbe reduced in an efficient and economical manner, and fine ironparticles dropping through the holes of a gas distributor can becirculated back into the fluidized bed furnace, thereby preventing animpediment of the reducing gas flow due to abnormalities such asdefluidizing or channeling.

In achieving the above object, the 2-stage fluidized bed type apparatusfor drying, pre-heating and pre-reducing a fine iron ore in a firstfluidized bed type furnace, and for finally reducing the fine iron ore(thus pre-reduced) in a second fluidized bed type furnace according tothe present invention includes:

a first tapered fluidized bed type furnace for receiving a raw fine ironore and a reducing gas to form a turbulent or bubbling fluidized bed soas to pre-heat and pre-reduce the raw iron ore;

a first cyclone for separating fine iron ore particles from a dischargegas of the first fluidized bed type furnace to recycle the separatedfine iron ore particles into the first fluidized bed type furnace, theseparated discharge gas of the first fluidized bed type furnace beingdischarged to external atmosphere;

a second fluidized bed type furnace for finally reducing the fine ironore (thus pre-heated and pre-reduced) of the first fluidized bed typefurnace, by forming a bubbling or turbulent fluidized bed by utilizing adischarge gas (reducing gas) of a melter-gasifier;

a second cyclone for separating fine iron ore particles from a dischargegas of the second fluidized bed type furnace to recycle the fine ironore particles into the bottom of the second fluidized bed type furnace,the separated discharge gas of the second fluidized bed type furnacebeing supplied to the first fluidized bed type furnace as a reducinggas;

a first intermediate hopper positioned between the first and secondfluidized bed type furnaces, for storing fine iron ore particles(dropped through the holes of a gas distributor of the first fluidizedbed type furnace) to recycle them into the lower portion of the secondfluidized bed type furnace; and

a second intermediate hopper positioned beneath the second fluidized bedtype furnace, for storing fine iron ore particles (dropped through theholes of a gas distributor of the second fluidized bed type furnace) torecycle them into the lower portion of the second fluidized bed typefurnace.

In another aspect of the present invention, the method for reducing afine iron ore by using the above reducing apparatus according to thepresent invention is characterized in that: a first fluidized bed typefurnace dries, pre-heats and pre-reduces the fine iron ore under areducing atmosphere; a second fluidized bed type furnace finally reducesthe pre-reduced fine iron ore; a hopper and a gas/solid particle sealingvalve are installed beneath each of the fluidized bed type furnaces; andthe fine iron ore particles dropping through the holes of the gasdistributors during an abnormality of operation are circulated back intothe fluidized bed type furnaces, whereby impediment of the gas flow isavoided.

BRIEF DESCRIPTION OF THE DRAWINGS

The above object and other advantages of the present invention willbecome more apparent by describing in detail the preferred embodiment ofthe present invention with reference to the attached drawings in which:

FIG. 1 illustrates a conventional single stage fluidized bed typefurnace;

FIG. 2 illustrates the conventional 3-stage fluidized bed type furnace;and

FIG. 3 illustrates the 2-stage fluidized bed type fine iron ore reducingfurnace according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIG. 3, the 2-stage fluidized bed type fine iron orereducing apparatus according to the present invention includes:

a first tapered fluidized bed type furnace 100 for receiving raw fineiron ore from a hopper 700 and for receiving a reducing gas to form aturbulent or bubbling fluidized bed so as to pre-heat and pre-reduce theraw iron ore;

a first cyclone 300 for separating fine iron ore particles from adischarge gas of the first fluidized bed type furnace 100 to recycle thefine iron ore particles into the first fluidized bed type furnace 100,the separated discharge gas of the first fluidized bed type furnacebeing discharged to the external atmosphere;

a second fluidized bed type furnace 200 for finally reducing the fineiron ore (thus pre-heated and pre-reduced) of the first fluidized bedtype furnace 100, by forming a bubbling or turbulent fluidized bed byutilizing a discharge gas (reducing gas) of a melter-gasifier 800;

a second cyclone 400 for separating fine iron ore particles from anexhaust gas of the second fluidized bed furnace 200 to recycle the fineiron ore particles into the bottom of the second fluidized bed furnace200, the separated discharge gas of the second fluidized bed furnace 200being supplied to the first fluidized bed furnace 100 as a reducing gas;

a first intermediate hopper 500 positioned between: the first and secondfluidized bed type furnaces 100 and 200, for storing fine iron oreparticles (dropped through the holes of a gas distributor 102 of thefirst fluidized bed type furnace 100) to recycle them into the lowerportion of the second fluidized bed type furnace 200; and

a second intermediate hopper 600 positioned beneath the second fluidizedbed type furnace 200, for storing fine iron ore particles (droppedthrough the holes of a gas distributor 202 of the second fluidized bedtype furnace 200) to recycle them into the lower portion of the secondfluidized bed type furnace 200.

The first fluidized bed type furnace 100 includes a lower taperedportion 100 a and an upper cylindrical portion 100 b. Further, a firstgas supply hole 101 is formed on the lower portion of the furnace 100 a,for receiving a reducing gas, and within the lower portion of thefurnace 100 a, there is installed a first gas distributor 102. Further,a first iron ore discharge hole 106 is formed on the side wall of thetapered portion, and the first iron ore discharge hole 106 communicatesthrough a second pipe 103 to the lower portion of the second fluidizedbed type furnace 200.

Further, an iron ore supply hole 105 is formed on the side wall of thetapered portion 100 a, and the iron ore supply hole 105 is connectedthrough a first pipe 701 to a hopper 700 to supply the fine iron oreinto the first fluidized bed type furnace 100. Further, a first gasdischarge hole 107 is formed on the top of the furnace 100, and thisfirst gas discharge hole 107 communicates through a third pipe 301 tothe upper portion of the first cyclone 300.

The first cyclone 300 separates the fine iron ore particles from thedischarge gas of the first fluidized bed furnace 100. On the bottom ofthe first cyclone 300, there is connected a fourth pipe 302 throughwhich the separated fine iron ore particles are circulated back to thelower portion of the first fluidized bed furnace 100. A fifth pipe 303is connected to the top of the first cyclone 300 which finally exhauststhe discharge gas from the first fluidized bed furnace 100.

The fourth pipe 302 is deeply buried into the first fluidized bed typefurnace 100 to recycle the separated fine iron ore particles deeply intothe first fluidized bed type furnace 100.

The second fluidized bed type furnace 200 includes a lower taperedportion 200 a and an upper cylindrical portion 200 b. A second gassupply hole 201 is formed on the lower portion of the tapered portion200 a, for receiving a reducing gas, and a gas distributor 202 isdisposed in the lower portion of the tapered portion 200 a.

A second iron ore discharge hole 206 is formed on the side wall of thetapered portion 200 a, and the second iron ore discharge hole 206communicates through an eighth pipe 203 into the melter-gasifier 800.

Further, a pre-reduced iron ore supply hole 205 is formed on the sidewall of the tapered portion 200 a, and the pre-reduced iron ore supplyhole 205 is connected through the second pipe 103 to the first fluidizedbed type furnace 100 to receive the dried, pre-heated and pre-reducediron ore into the second fluidized bed type furnace 200. A second gasdischarge hole 207 is formed on the top of the furnace 200, and thissecond gas discharge hole 207 communicates through a 10th pipe 401 tothe second cyclone 400.

The second cyclone 400 separates the fine iron ore particles from thedischarge gas of the second fluidized bed type furnace 200. A 9th pipe402 is connected from the bottom of the second cyclone 400 to the lowerportion of the furnace 200, for circulating the separated fine iron oreparticles into the furnace 200. A 6th pipe 403 is connected to the topof the second cyclone 400, for supplying the discharge gas of the secondfluidized bed type furnace 200 to the first fluidized bed type furnace100.

The 9th pipe 402 should be preferably buried deeply into the secondfluidized bed type furnace 200 to recycle the separated fine iron oreparticles deeply into its interior.

The first intermediate hopper 500 is disposed between the firstfluidized bed type furnace 100 and the second fluidized bed type furnace200. The hopper 500 is connected through a seventh pipe 502 to thebottom of the first fluidized bed type furnace 100, and is connectedthrough an 11th pipe 504 into the second fluidized bed type furnace 200.

On the 7th pipe 502 and the 11th pipe 504, there are installed one ormore of gas/solid sealing type high temperature valves 501 and 503. Inthis way, during an emergency situation such as a sudden stop ofoperation or the like, the fine iron ore particles which have beendropped through the holes of the gas distributor 102 of the firstfluidized bed type furnace 100 can be temporarily stored, and thentransported by an inactive gas such as nitrogen into the secondfluidized bed type furnace 200.

The 11th pipe 504 should be preferably deeply buried into the secondfluidized bed type furnace 200, and thus, the fine iron ore particleswhich have been dropped through the holes of the gas distributor 102 ofthe first fluidized bed type furnace 100 can be recycled deeply into thesecond fluidized bed type furnace 200.

The second intermediate hopper 600 is disposed beneath the secondfluidized bed type furnace 200, and is connected through a 13th pipe 602to the bottom of the second fluidized bed type furnace 200, while thehopper 600 is connected through a 12th pipe 604 to the lower portion ofthe second fluidized bed type furnace 200.

On the 13th pipe 602 and the 12th pipe 604 (i.e., upstream anddownstream of the hopper 600), there are installed one or more gas/solidsealing type high temperature valves 601 and 603. In this way, during anemergency situation such as a sudden stop of operation or the like, thefine iron ore particles which have been dropped through the holes of thegas distributor 202 of the second fluidized bed type furnace 200 can betemporarily stored, and then transported by an inactive gas such asnitrogen into the second fluidized bed type furnace 200.

Now the method for reducing a fine iron ore by using the above describedreducing apparatus will be described.

A fine iron ore which is supplied to the first fluidized bed typefurnace 100 is pre-heated and pre-reduced by using a discharge gas(reducing gas) of the second fluidized bed type furnace 200, whileforming a bubbling or turbulent fluidized bed. The iron ore thus reactedis transferred through a second pipe 103 to the lower portion of thesecond fluidized bed type furnace 200. Then a final reduction occurswithin the second fluidized bed type furnace 200 by forming a bubblingfluidized bed by using a discharge gas (a discharge gas of themelter-gasifier) which is supplied through the second gas supply hole201. The finally reduced iron is discharged through the second iron oredischarge hole 206. The fine iron ore particles which are entrained inthe discharge gas of the first fluidized bed type furnace 100 areseparated from the gas by the first cyclone 300 to be circulated back tothe lower portion of the first fluidized bed type furnace 100. The fineiron ore particles which are entrained in the discharge gas of thesecond fluidized bed type furnace 200 are separated from the gas by thesecond cyclone 400 to be circulated back to the lower portion of thesecond fluidized bed type furnace 200.

In the present invention, if an abnormality such as defluidizing orchannelling occurs during the operation of the fluidized bed typefurnaces, the fine iron ore particles drop through the holes of the gasdistributor to impede the flow of the reducing gas. Therefore,periodically during the operation and at an emergency such as theblocking of the reducing gas, first the high temperature valves 501 and601 (upstream of the first and second intermediate hoppers 500 and 600)are opened. Thus the fine iron ores which are accumulated beneath thegas distributors of the first and second fluidized bed type furnaces 100and 200 are transferred to the first and second intermediate hoppers 500and 600, respectively, to be stored there. Then the upstream valves 501and 601 are closed, and the valves 503 and 603 (downstream of the firstand second intermediate hoppers 500 and 600) are opened. Then aninactive gas such as nitrogen is injected to circulate back the storediron ore into the second fluidized bed type furnace 200.

When the 2-stage fluidized bed type reducing furnace is used to reduce afine iron ore, the pre-heating and the pre-reducing within the firstfluidized bed type furnace 100 should be carried out preferably at700-850° C., and the final reaction within the second fluidized bed typefurnace 200 should be carried out preferably at 750-900° C. Theoperating pressure should be preferably 1-5 atmospheres in the absolutepressure. The superficial gas velocity right above the gas distributorswithin the first and second fluidized bed type furnaces 100 and 200should be preferably 1.2-2.5 times as fast as the minimum fluidizationvelocity of the fine iron ore staying within the furnaces, in view ofthe efficient fluidizing and the elutriation loss of the iron oreparticles. The angle of the tapered portions should be preferably 5-20°C. relative to the vertical line. The height of the tapered portions 100a and 200a above the gas distributors should be preferably 5-10 times aslarge as the diameter of the gas distributors. The height of thecylindrical portions 100 b and 200 b should be preferably 3-5 times aslarge as their own inner diameter.

Now the present invention will be described in detail based on an actualexample.

EXAMPLE

A reduction of a fine iron ore was carried out by using a reducingapparatus having a size as shown in Table 1 and at conditions set forthin Tables 2 to 4.

TABLE 1 Height and ID of fluidized bed type furnace First fluidized IDof tapered portion (at the surface bed type furnace of gas distributor):0.6 m Angle of tapered portion: 5° Height of tapered portion (from gasdistributor): 3 m ID of cylindrical portion: 1.1 m Height of cylindricalportion: 3.5 m Second fluidized ID of tapered portion (at the surfacebed type furnace of gas distributor): 0.6 m Angle of tapered portion: 5°Height of tapered portion (from gas distributor): 3 m ID of cylindricalportion: 1.1 m Height of cylindrical portion: 3.5 m

TABLE 2 Chemical composition and particle size distribution of the ironore 1. Chemical composition: 62.17 of T.Fe, 0.51 of FeO, 5.5 of SiO₂,0.11 of TiO₂, 0.05 of Mn, 0.012 of S, 0.65 of P, 2.32 of moisture 2.particle size distribution: 4.6% of −0.05 mm, 5.4% of 0.05-0.15 mm,16.8% of 0.15-0.5 mm, 59.4% of 0.5-4.75 mm, 13.8% of 4.75-8 mm

TABLE 3 Ingredients, temperature and pressure of reducing gas 1. Gasingredients: 65% of CO, 25% of H₂, 5% of CO₂, 5% of N₂ 2. Temperature:800° C. for pre-heating and pre-reducing 850° C. for final reduction 3.Pressure: 1.8 Kgf/cm² for pre-heating and pre-reducing 2.0 Kgf/cm² forfinal reduction

TABLE 4 Superficial Gas velocity in fluidized bed type furnace Firstfluidized Velocity at the surface of gas bed type furnace distributor:1.4 m/s Velocity in cylindrical portion (superficial velocity): 0.4 m/sSecond fluidized Velocity at the surface of gas bed type furnacedistributor: 1.4 m/s Velocity in cylindrical portion (superficialvelocity): 0.4 m/s

After reducing the fine iron ore by using the above specified apparatusand at conditions set forth in the above tables, the average gasutilization degree and the gas consumption rate were evaluated. Theresult showed that the gas utilization degree was about 30-35%, and thegas consumption rate was 1200-1500 Nm³/ton-ore. Further, the reductionrates of the reduced irons which were discharged through the first andsecond discharge holes were respectively 30-40% and 85-95%. The iron oredischarge was possible after 60 minutes from feeding the iron orethrough the hopper. This shows that the reducing speed is veryexcellent.

According to the present invention as described above, intermediatehoppers and gas/solid sealing valves are installed beneath the fluidizedbed type furnaces. Thus the fine iron ore particles which drop throughthe holes of the gas distributors during an abnormality of operation canbe circulated back to the fluidized bed type furnaces. Therefore, theflow of the reducing gas is never impeded, and therefore, the operationcan be carried out for a long time without a halt.

Further, with only the 2-stage process, the present invention ensures asufficient reduction rate and a superior gas consumption rate, and isnot inferior to Korean Patent 117065 (1997). Further, the presentinvention is superior over Korean Patent 117065 (1997) in the facilitycost and the production cost.

Further, in the present invention, a relatively uniformly reduced ironcan be obtained regardless of the particle sizes of the iron ore.Further, the discharge amounts and particle sizes can be adjusted forthe respective discharge holes, and the reduction rate can be adjustedby controlling the residence time of the iron ore within the furnace.

What is claimed is:
 1. A two-stage fluidized bed apparatus for drying,pre-heating and pre-reducing a fine iron ore in a first fluidized bedfurnace, and for finally reducing the pre-reduced fine iron ore in asecond fluidized bed furnace, comprising: a first tapered fluidized bedfurnace for receiving a raw fine iron ore from a hopper through a firstgas supply hole and for receiving a reducing gas to form a turbulent orbubbling fluidized bed so as to pre-heat and pre-reduce the raw iron oreand so as to discharge the fine iron ore thus pre-reduced through afirst ore discharge hole; a first cyclone for separating fine iron oreparticles from a discharge gas of said first fluidized bed furnace torecycle the fine iron ore particles thus separated into said firstfluidized bed furnace; a second fluidized bed furnace for finallyreducing the pre-heated and pre-reduced fine iron ore of said firstfluidized bed furnace, by forming a bubbling or turbulent fluidized bedby utilizing a discharge gas supplied from a melter-gasifier through asecond gas supply hole, a finally reduced iron being discharged througha second iron ore discharge hole; a second cyclone for separating fineiron ore particles from a discharge gas of said second fluidized bedfurnace to recycle the fine iron ore particles thus separated into abottom of said second fluidized bed furnace; a first intermediate hopperpositioned between said first and second fluidized bed furnaces, forstoring fine iron ore particles, which have been dropped through holesof a gas distributor of said first fluidized bed furnace, to recyclethem into a lower portion of said second fluidized bed furnace; a secondintermediate hopper positioned beneath said second fluidized bedfurnace, for storing fine iron ore particles, which have been droppedthrough holes of a gas distributor of said second fluidized bed furnaceto recycle them into a lower portion of said second fluidized bedfurnace; said first ore discharge hole communicating by way of a pipewith said pre-reduced iron ore supply hole; said first gas dischargehole communicating by way of a pipe with an upper portion of said firstcyclone, and said first cyclone being connected by way of a pipe withsaid first tapered fluidized bed furnace; said second cyclone beingconnected by way of a pipe with a top of said second fluidized bedfurnace, connected by way of a pipe with a lower portion of said secondfluidized bed furnace, and connected by way of a pipe with a lowerportion of said first fluidized bed furnace; said first intermediatehopper being connected by way of a pipe with a lower portion of saidfirst fluidized bed furnace, and connected by way of a pipe with aninterior of said second fluidized bed furnace; and said secondintermediate hopper being connected by way of a pipe with a bottom ofsaid second fluidized bed furnace, and connected by way of a pipe with alower portion of said second fluidized bed furnace.
 2. The two-stagefluidized bed fine iron ore reducing apparatus as claimed in claim 1,wherein: a discharge end of said pipes connecting said first and secondcyclones with the respective first and second fluidized bed furnaces aredeeply buried into a lower portion of said respective first and secondfluidized bed furnaces to recycle the fine iron ore particles, whichhave been dropped through holes of said gas distributor, deeply into thelower portion of said respective first and second fluidized bedfurnaces.
 3. The two-stage fluidized bed fine iron ore reducingapparatus as claimed in claim 1, wherein selected pipes in the apparatusare respectively provided with gas/solid sealing high temperaturevalves.
 4. The two-stage fluidized bed fine iron ore reducing apparatusas claimed in claim 1, wherein said first fluidized bed furnace and saidsecond fluidized bed furnace respectively comprise a tapered portion anda cylindrical portion; wherein said tapered portion has an inclinationangle of 5-20° C. relative to a vertical line; said tapered portion hasa height above said gas distributor which is 5-10 times as large as adiameter of said gas distributor; and said cylindrical portion has aheight 3-5 times as large as its inside diameter.
 5. The two-stagefluidized bed fine iron ore reducing apparatus as claimed in claim 1,wherein said first fluidized bed furnace and said second fluidized bedfurnace respectively comprise a tapered portion and a cylindricalportion; wherein said tapered portion has an inclination angle of 5-20°C. relative to a vertical line; said tapered portion has height abovesaid gas distributor which is 5-10 times as large as a diameter of saidgas distributor; and said cylindrical portion has a height 3-5 times aslarge as its inside diameter.
 6. A method for reducing a fine iron oreby using a two-stage fluidized bed apparatus for drying, pre-heating andpre-reducing a fine iron ore in a first fluidized bed furnace, and forfinally reducing the pre-reduced fine iron ore in a second fluidized bedfurnace, comprising the steps of: drying, pre-heating and pre-reducing afed fine iron ore within a first fluidized bed furnace while forming abubbling or turbulent fluidized bed by utilizing a discharge gas from asecond fluidized bed furnace, transferring the pre-reduced fine iron orethrough a pipe to a lower portion of said second fluidized bed furnace,and finally reducing the iron ore by forming a bubbling fluidized layerby utilizing a reducing gas supplied from a melter-gasifier through adischarge gas supply hole; separating extremely fine iron ore particlesfrom a discharge gas of said first fluidized bed furnace by a firstcyclone to circulate back the separated fine iron ore particles to alower portion of said first fluidized bed furnace, and separatingextremely fine iron ore particles from a discharge gas of said secondfluidized bed furnace by a second cyclone to circulate back theseparated fine iron ore particles to a lower portion of said secondfluidized bed furnace; and opening upstream high temperature valves offirst and second intermediate hoppers at an emergency situation to storeaccumulated fine iron ore particles in said first and secondintermediate hoppers, then closing said upstream high temperature valvesand opening downstream high temperature valves of said first and secondintermediate hoppers, and injecting an inactive gas to transfer the fineiron ore particles to a lower portion of said second fluidized bedfurnace.
 7. The method as claimed in claim 6, wherein a gas flowvelocity just above said gas distributors of said first and secondfluidized bed furnaces is 1.2-2.5 times as fast as a minimumfluidization velocity of the fine iron ore particles staying within saidfurnaces.
 8. The method as claimed in claim 6, wherein a pre-heating anda pre-reducing are carried out within said first fluidized bed furnaceat a temperature of 700°-850° C., a final reduction is carried outwithin said second fluidized bed furnace at a temperature of 750-900°C., and an operating pressure of 1-5 atmospheres in absolute pressure isapplied to the respective furnaces.
 9. The two-stage fluidized bed fineiron ore reducing apparatus as claimed in claim 2, wherein selectedpipes in the apparatus are respectively provided with gas/solid sealinghigh temperature valves.
 10. The two-stage fluidized bed fine iron orereducing apparatus as claimed in claim 2, wherein said first fluidizedbed furnace and said second fluidized bed furnace respectively comprisea tapered portion and a cylindrical portion; wherein said taperedportion has an inclination angle of 5-20° C. relative to a verticalline; said tapered portion has a height above said gas distributor whichis 5-10 times as large as a diameter of said gas distributor; and saidcylindrical portion has a height 3-5 times as large as its insidediameter.
 11. The two-stage fluidized bed fine iron ore reducingapparatus as claimed in claim 9, wherein said first fluidized bedfurnace and said second fluidized bed furnace respectively comprise atapered portion and a cylindrical portion; wherein said tapered portionhas an inclination angle of 5-20° C. relative to a vertical line; saidtapered portion has a height above said gas distributor which is 5-10times as large as a diameter of said gas distributor; and saidcylindrical portion has a height 3-5 times as large as its insidediameter.
 12. The two-stage fluidized bed fine iron ore reducingapparatus as claimed in claim 7, wherein selected pipes in the apparatusare respectively provided with gas/solid sealing high temperaturevalves.